2. Fire and high pressure laminate cladding
The term 'cladding' refers to components that are attached to the primary structure of a building to form non-structural, external surfaces as opposed to buildings in which the external surfaces are formed by structural elements, such as masonry walls.
2.1 Fire classification
The Euroclass system, of BS EN 13501-1, is recognised as the standard to determine the reaction to fire performance of materials across Europe. It classifies the reaction to fire, as well as evaluating multiple aspects such as ignitability, flame spread, heat release, smoke production and propensity for producing flaming droplets/particles. The reaction to fire tests are scenario tests ranging from small scale material tests to intermediate scale tests typically used to assess the fire performance of internal wall and ceiling linings. In the absence of a large scale façade systems test, these tests are often used by regulators to classify the fire performance of façade systems. The European Commission are currently developing a large scale façade system test and preliminary work on this standard is expected to be completed in 2022.
Reaction to fire classes for surface coverings and insulation materials that may be installed behind the surface are divided into seven main classes, as A1 (or non-combustible), which is the best performance through A2 (will not significantly contribute to fire load and fire growth), B, C, D, E and to finally F, the worst fire performance.
As well as reaction to fire, smoke development (classifications lowest to highest - s1, s2 and s3) and the formation of flaming droplets/particles (classifications lowest to highest - d0, d1 and d2) are measured and declared.
Prior to the introduction of European Standards the British Standard, BS 476, was used as the basis of the classification of fire performance. Whilst the building standards no longer refer to BS 476 the relevant parts cited in earlier editions of the technical standards and guidance were as follows:
- BS 476: Part 4 describes the non-combustibility test for materials. The test measures temperature rise and flaming of test specimens under standard heating conditions using a small furnace. Materials that do not meet specified conditions in the standard were deemed combustible.
- BS 476: Part 6 describes a method of testing for the ﬁre propagation of products. The standard specifies the method to determine the fire propagation index of materials and was used primarily for internal wall and ceiling linings.
- BS 476: Part 7 describes the method of testing to determine the classiﬁcation of the surface spread of ﬂame of products. The standard specifies the test to measure the lateral spread of flame along the surface of a product and gives the related classification system for essentially flat materials, composites or assemblies and was used primarily for the exposed surfaces of walls or ceilings (Classes 1 to 4).
- BS 476: Part 11 describes a method for assessing the heat emission from building materials. Any material that does not flame or cause any rise in temperature on either the centre of the test specimen or the furnace thermocouples were deemed to be non-combustible.
A Class O product was a classification deﬁned in the relevant building regulations rather than the British Standards. Until the introduction of the European Standards, Class O was one of the highest fire performance classifications that could be obtained by products, and is described by the following:
- The surface material (or where it is bonded throughout to a substrate, the surface material combined with the substrate) has a surface of Class 1 when tested in accordance with BS 476-7: 1997 and has an index of performance (I) not more than 12 and a sub-index (i 1) not more than 6 when tested in accordance with BS 476: Part 6: 1981(1989).
Note: Any product that meets the criteria for a 'non-combustible' classification when tested in accordance with BS 476-4 or assessed in accordance with BS 476-11 achieves the highest possible product classification for reaction to fire.
2.2 High pressure laminate
High pressure laminate (HPL) panels are a form of cladding panel typically manufactured by layering sheets of wood or paper fibre with a resin and bonding them under heat and pressure. They sometimes include additional chemicals to provide fire retardant properties and are available in a wide range of colours and finishes.
Panels which incorporate fire retardant chemicals are sometimes referred to as "FR grade" and these will typically achieve European Standard Classification B-s1, d0. Panels manufactured without fire retardant chemicals are typically Class C or D, depending on the thickness of the panel.
Following the Grenfell Tower Fire and subsequent concerns regarding the fire performance of cladding panels (in particular Aluminium Composite Material (ACM) cladding), the Ministry of Housing, Communities and Local Government (MHCLG) conducted a BS 8414 test of a cladding system comprising an HPL panel with fire retardant (Class B-s1, d0) together with stone wool insulation and fire barriers. This system specification achieved the performance criteria set out in BR135 Fire performance of external thermal insulation for walls of multi-storey buildings. As a result, MHCLG's Independent Expert Advisory Panel (IEAP) consider this combination of materials can be safe on existing buildings, depending on the composition of the entire cladding systems and how it is fitted.
The Scottish Advice Note (2021) has taken a similar view using the evidence provided by the BS 8414 test. However according to the IEAP, HPL panels of Class C or D are unlikely to adequately resist the spread of fire regardless of the type of insulation material exposed behind the cladding. In addition, the IEAP suggest that systems using any type of HPL panels of Class B with combustible insulation are also unlikely to adequately resist the spread of fire.
The level of risk from HPL systems is not as high as the risk from systems using aluminium composite material panels with a polyethylene core (Category 3). Extensive experimental fire testing in a MHCLG sponsored programme has validated the opinion of the expert panel on this matter.
Note that when the solid constituent parts of HPL panels are tested in the bomb calorimeter, they typically provide a gross heat of combustion of circa 20 Mega Joules per kilogram (MJ/kg) in accordance with BS EN ISO 1716: 2018. The core material used in thin category 3 ACM(PE) panels typically achieve more than double the HPL value at circa 45 MJ/kg.
In conclusion, where HPL panels are installed on buildings, test evidence should be sought which may include small scale, intermediate scale or large scale fire test data. Appropriate panel fixings, support rails and fire barriers within the cavity are extremely important when determining the fire performance of the cladding system. The information gathered should be taken account as part of the holistic fire risk assessment to determine the safety of the building occupants in the case of fire.